Metal chloride gas generator, hydride vapor phase epitaxy growth apparatus, and nitride semiconductor template

ABSTRACT

A nitride semiconductor template includes a substrate, and a chlorine-containing nitride semiconductor layer. The chlorine-containing nitride semiconductor layer contains an iron concentration of not higher than 1×10 17  cm −3 .

The present application is a Divisional application of U.S. patentapplication Ser. No. 13/569,983, filed on Aug. 8, 2012, which is basedon and claims priority from Japanese patent application No. 2011-178413filed on Aug. 17, 2011, the entire contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a metal chloride gas generator, a hydridevapor phase epitaxy growth apparatus, and a nitride semiconductortemplate.

2. Description of the Related Art

Gallium nitride compound semiconductors, such as gallium nitride (GaN),aluminum gallium nitride (AlGaN), and indium gallium nitride (InGaN)have attracted attention as light-emitting device materials capable ofred through ultraviolet light emission. One growing method for thesegallium nitride compound semiconductor crystals is a Hydride Vapor PhaseEpitaxy (HYPE) growing method using metal chloride gas and ammonia asraw material.

A feature of the HVPE method is as follows. According to this method, itis possible to obtain a growth rate of 10 μm/hr to 100 μm/hr or higherwhich is remarkably higher than a typical growth rate of several μm/hrin other growing methods such as Metal Organic Vapor Phase Epitaxy(MOVPE) and Molecular Beam Epitaxy (MBE). For this reason, the HVPEmethod has been often used in the manufacture of a GaN free-standingsubstrate (see e.g. JP Patent No. 3886341) and an AlN free-standingsubstrate. Here, the term “free-standing substrate” refers to asubstrate having such strength to hold its own shape and not to causeinconvenience in handling.

In addition, a light-emitting diode (LED) made of a nitridesemiconductor is typically formed over a sapphire substrate. In itscrystal growth, after a buffer layer is formed over a surface of thesubstrate, a GaN layer having a thickness of the order of 10 to 15 μmincluding an n-type layer is grown thereover, and an InGaN/GaN multiplequantum well light-emitting layer (several hundreds nm thick in total)and a p-type layer (200 to 500 nm thick) are grown thereover in thisorder. The GaN layer under the light-emitting layer is thick in order toimprove the crystallinity of GaN on the sapphire substrate and the like.This is followed by electrode formation, resulting in a final devicestructure as shown in FIG. 7 which will be described later. In the caseof growth with the MOVPE method, the crystal growth typically requiresabout 6 hours, and about half of 6 hours is the time required to grow aso-called “template portion” that are nitride semiconductor layer(s)e.g. GaN layer(s) under the light-emitting layer.

From the above, it is supposed, if it is possible to apply the HVPEmethod with the remarkably high growth rate to the growth of thetemplate, it will be possible to substantially shorten the growth time,thereby dramatically reduce LED wafer manufacturing cost. In growing thetemplate portion with the HVPE method which can lower the productioncost, however, due to contamination by many unintended impurities, it isdifficult to fabricate the good quality template.

For the HVPE apparatus used for manufacturing the nitride semiconductor,Ga, NH₃ gas, HCl gas are generally used as main raw material. Inaddition, the growth temperature required for effectively forming a filmis a high temperature, namely, not lower than 1000 degrees Celsius. Forthis reason, a material to be used for a gas inlet pipe and a reactor ise.g. quartz that is chemical resistant and heat resistant to NH₃ gas andHCl gas that are highly reactive at high temperature. Specifically, theHVPE apparatus has a structure as shown in FIG. 8 which will bedescribed later, and has a tube reactor made of quartz divided into araw material section on its upstream side (i.e. upstream raw materialsection) and a growing section on its downstream side (i.e. downstreamgrowing section), and an upstream open end of the reactor is closed byan upstream flange made of stainless steel (SUS), and the gas inletpipes made of quartz are installed through the upstream flange from theraw material section towards the growing section. Because the gas inletpipes made of quartz cannot be attached directly to the upstream flange,a pipe made of SUS is connected to an outer side of an upstream end ofeach of the gas inlet pipes, and this pipe is attached to the upstreamflange (see e.g. JP-A-2002-305155).

SUMMARY OF THE INVENTION

In the above-configured HVPE apparatus, however, radiant heat from thegrowing section the temperature of which is the highest in the apparatusis conducted to the pipe, so that the temperature of the pipe portion isalso high. When the temperature of the pipe is high, the gas flowingthrough the pipe tends to react with the constituent material of thepipe, and the constituent material of the pipe may be scraped off(corroded) by this gas, and the nitride semiconductor template may becontaminated with this corroded constituent material of the pipe portionas unintended impurities. Particularly, the impurity contaminations aresignificantly due to interfusion of impurities from the pipe portionthrough which the corrosive NH₃ or HCl gas flows.

Through the specification and claims, the “nitride semiconductortemplate” or simply “template” means a device which includes a substrateand nitride semiconductor layer(s) e.g. GaN layers to be provided undera light-emitting layer, and may further include a buffer layer or thelike. Further, the “template portion” means the nitride semiconductorlayer(s) in the “nitride semiconductor template”.

Accordingly, it is an object of the present invention to provide a metalchloride gas generator, a hydride vapor phase epitaxy growth apparatus,and a nitride semiconductor template that suppress interfusion ofunintended impurities into the nitride semiconductor template.

As a result of earnest study to achieve the above described problem, theinventors have found that the nitride semiconductor template made byusing the metal chloride gas generator to be used at not lower than1000° C. is contaminated by unintended impurities because theconstituent material of the pipe is corroded by the gas flowing in thehigh temperature SUS pipe at the gas inlet and interfuses into thetemplate as the unintended impurities.

By reducing the radiant heat from the heater, it is possible to suppressthe rise in temperature of the SUS pipe portion at the gas inlet to someextent. The Inventors however found that the above-mentioned method hasa limit. The reason thereof can be described as follows. The Inventorsfound that the contamination by unintended impurities is caused by theeffect of the high temperature of the SUS pipe portion at the gas inletdue to the gas inlet pipe acting as an optical waveguide, morespecifically, because the quartz material of the above gas inlet pipe isa light transmissive material. Here, the “optical waveguide phenomenon”refers to a radiant heat waveguiding phenomenon due to the gas inletpipe acting as an optical waveguide.

For this reason, in order to suppress the temperature rise in the SUSpipe portion at the gas inlet, heat shield plate(s) are first providedbetween the growing section at the highest temperature and the gas inletto suppress the temperature rise due to the radiant heat. In addition,the Inventors found that the contamination by impurities is suppressedby bending a portion of the gas inlet pipe between the heat shieldplate(s) (more specifically, the heat shield plate which is closer tothe gas inlet) and the upstream end (more specifically, the gas inlet)to change the position of the gas inlet to suppress the temperature risein the SUS pipe portion at the gas inlet. The radiant heat caused at thedownstream side of the gas inlet pipe (specifically, the radiant heatfrom the growing section of the metal chloride gas generator) issuppressed by the heat shield plate(s) and the bent structure of the gasinlet pipe, and the heat is less likely to be conducted to the upstreamend to suppress the temperature rise in the upstream end. According tothis structure, the gas introduced from the gas inlet pipe is suppressedfrom being contaminated by the constituent material of the pipe asimpurities at the upstream end.

According to a feature of the invention, a metal chloride gas generatorcomprises:

a tube reactor including a receiving section for receiving a metal on anupstream side, and a growing section in which a growth substrate isplaced on a downstream side;

a gas inlet pipe arranged to extend from an upstream end with a gasinlet via the receiving section to the growing section, for introducinga gas from the upstream end to supply the gas to the receiving section,and supplying a metal chloride gas produced by a reaction between thegas and the metal in the receiving section to the growing section; and

a heat shield plate placed in the reactor to thermally shield theupstream end from the growing section,

wherein the gas inlet pipe is bent between the upstream end and the heatshield plate.

According to another feature of the invention, a hydride vapor phaseepitaxy growth apparatus comprises:

the above-defined metal chloride gas generator.

According to a still another feature of the invention, a nitridesemiconductor template comprises:

a substrate; and

a chlorine-containing nitride semiconductor layer,

wherein the chlorine-containing nitride semiconductor layer contains aniron concentration of not higher than 1×10¹⁷ cm⁻³.

Effects of the Invention

According to the present invention, it is possible to suppressinterfusion of unintended impurities into the nitride semiconductortemplate.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments according to the invention will be explainedbelow referring to the appended drawings, wherein:

FIG. 1 is a diagram showing an example of schematic configuration of anHYPE apparatus in a first embodiment according to the present invention;

FIG. 2 is a cross-sectional view showing a nitride semiconductortemplate in a second embodiment according to the present invention;

FIG. 3 is a graph showing a result of SIMS analysis of Fe;

FIG. 4 is a graph showing a result of SIMS analysis of Cr;

FIG. 5 is a graph showing a result of SIMS analysis of Ni;

FIG. 6 is a cross-sectional view showing a semiconductor light-emittingdevice epitaxial wafer in this embodiment;

FIG. 7 is a cross-sectional view showing a semiconductor light-emittingdevice in an example according to the present invention;

FIG. 8 is a diagram typically showing an HVPE apparatus in comparativeexample 1; and

FIG. 9 is a cross-sectional view illustrating a Schottky barrier diodein variation 4 according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, preferred embodiments according to the invention will be describedin more detail in conjunction with the appended drawings. It should benoted that in each figure, for components having substantially the samefunctions, duplicate description thereof will be omitted given the samereference numerals.

SUMMARY OF THE EMBODIMENT

A metal chloride gas generator in this embodiment comprises a tubereactor including a receiving section for receiving a metal on anupstream side, and a growing section in which a growth substrate isplaced on a downstream side; a light transmissive gas inlet pipearranged to extend from an upstream end with a gas inlet via thereceiving section to the growing section, for introducing a gas from theupstream end to supply the gas to the receiving section, and supplying ametal chloride gas produced by a reaction between the gas and the metalin the receiving section to the growing section; and a heat shield plateplaced in the reactor to thermally shield the upstream end from thegrowing section. Specifically, the heat shield plate thermaticallyshields between an upstream end side portion of the gas inlet pipe and agrowing section side portion of the gas inlet pipe. The gas inlet pipeis configured to be bent between the upstream end and the heat shieldplate.

The above gas inlet pipe may introduce a chloride gas from the gasinlet. In addition, the above heat shield plate may comprise carbon orquartz. The above upstream end may comprise a metal.

Radiant heat from the growing section is prevented by the heat shieldplate to suppress a rise in temperature of the upstream end of the gasinlet pipe. The gas inlet pipe is configured to be bent between the heatshield plate and the upstream end, so that the radiant heat from thegrowing section is less likely to be conducted to the upstream end, andthe temperature of the upstream end is even further suppressed fromrising.

In addition, the hydride vapor phase epitaxy growth apparatus(hereinafter, referred to as “HVPE apparatus”) in this embodiment isequipped with the above described metal chloride gas generator. The gasinlet pipe included in the metal chloride gas generator may comprisequartz.

In addition, the nitride semiconductor template in this embodiment has asubstrate and a chlorine-containing nitride semiconductor layer, and thechlorine-containing nitride semiconductor layer contains an ironconcentration of not higher than 1×10¹⁷ cm⁻³. The nitride semiconductortemplate comprises a plurality of nitride semiconductor layers formedover a heterogeneous substrate, and made of a homogeneous materialdifferent from that of the heterogeneous substrate.

In the above nitride semiconductor, a full width at half maximum (FWHM)of a (0004) plane of X-ray diffiaction (XRD) is preferably not less than200 seconds and not more than 300 seconds. The above nitridesemiconductor template may have a Si-doped GaN layer containing a Siconcentration of not less than 5×10¹⁸ cm⁻³ and not more than 5×10¹⁹cm⁻³.

First Embodiment

FIG. 1 is a diagram showing an example of schematic configuration of anHVPE apparatus 1 in a first embodiment according to the presentinvention. This HVPE apparatus 1 is divided into a raw material section3 a on an upstream side and a growing section 3 b on a downstream side,which are heated by separate raw material section heater 4 a and growingsection heater 4 b to about 850 degrees Celsius and 1100 degreesCelsius, respectively.

In addition, an HVPE apparatus has a tube reactor 2, and an upstreamopen end of the reactor 2 is closed by an upstream flange 8A made ofstainless steel (SUS), while a downstream open end of the reactor 2 isclosed by a downstream flange 8B made of SUS. Four system gas supplylines 6 of a group V line 61, group III (for Al and Ga) line 62, and adoping line 63 are installed through the upstream flange 8A from the rawmaterial section 3 a towards the growing section 3 b.

The group V line 61, the group III line 62 and the doping line 63 areconstituted by the same gas inlet pipes 60. Each of the gas inlet pipes60 is arranged to extend from an upstream end 64 having a gas inlet 64 atowards the growing section 3 b. It should be noted that the group IIIline 62 is arranged to extend via a tank 7 as a receiving section (asdescribed later) towards the growing section 3 b. The upstream end 64 isformed of a metal such as SUS. The gas inlet pipe 60 made of quartz isformed of e.g. a light-transmissive high purity quartz. Because the gasinlet pipe 60 made of quartz cannot be attached directly to the upstreamflange 8A, the upstream end 64 having a pipe made of SUS connected to anouter side of an upstream end of each of the gas inlet pipes 60 isattached to the upstream flange 8A.

From the group V line 61, hydrogen, nitrogen, or a mixture of thesegases is supplied as a carrier gas together with ammonia (NH₃) as anitrogen raw material.

From the group III line 62, hydrogen, nitrogen, or a mixture of thesegases is supplied as a carrier gas together with hydrogen chloride (HCl)to provide chloride gas. In the middle of the Group III line 62, thetank 7 as a receiving section that receives a gallium metal (Ga) melt 7a is installed. In the tank 7, GaCl gas as metal chloride gas isgenerated by the reaction of Ga metal and HCl gas and sent to thegrowing section 3 b.

From the doping line 63, for the case that the doping is not carriedout, e.g., when an undoped GaN layer (un-GaN layer) 13 is grown, amixture gas of hydrogen and nitrogen is introduced, and when a Si-dopedGaN layer 14 is grown, dichlorosilane (diluted with hydrogen, 100 ppm)as a raw material of Si, HCl gas, hydrogen, and nitrogen are introduced.Further, from the doping line 63, when the baking process is carried outto remove GaN-based deposits attached in the HVPE apparatus 1 after theHVPE growth, HCl gas, hydrogen, and nitrogen are introduced.

In the growing section 3 b, a tray 5 which rotates at a rotational speedof about 3 to 100 r/min is installed, and a sapphire substrate 11 isinstalled on a plane (installation plane) 5 a which faces to a gasoutlet 60 a of each of the gas supply lines 6. The raw material gasflown from the sapphire substrate 11 towards the downstream side isevacuated through an exhaust pipe 2 a from a most downstream part. Thegrowth in the this embodiment and examples was carried out at normalpressure of 1.013×10⁵ Pa (1 atm).

The tank 7 and a rotation shaft 5 b of the tray 5 are made ofhigh-purity quartz, and the tray 5 is made of SiC coated carbon.

Further, in the HVPE apparatus 1, a first heat shield plate 9A isdisposed between the growing section 3 b a temperature of which is thehighest in the reactor 2 and the raw material section 3 a, and a secondheat shield plate 9B is disposed between the upstream flange 8A and thefirst heat shield plate 9A, in order to suppress the temperature risenear the entrance to the reactor 2 of the gas supply line 6, namely, tothermally shield the upstream end 64 from the growing section 3 b. Byplacing the first and second heat shield plates 9A, 9B between thegrowing section 3 b and the gas inlet 64 a of the gas supply line 6, itis possible to shield the radiant heat from the growing section 3 b bythe first and second heat shield plates 9A, 9B, thereby suppress thetemperature rise of a region in the vicinity of the gas inlet 64 a (theupstream end 64) of the gas supply line 6.

Further, the gas supply line 6 is bent (flexed) in the middle thereofsuch that a position thereof that passes through the first and secondheat shield plates 9A, 9B is substantially located in the vicinity of acenter in a radial direction of the reactor 2, while a position thereofthat passes through the upstream flange 8A is eccentrically located fromthe center in the radial direction of the reactor 2.

In other words, the structure of the gas supply line 6 is not a straightpipe structure but a bent structure, and the first and the second heatshield plates 9A, 9B are arranged between the growing section 3 b in ahigh temperature growing region and the gas inlet 64 a. The gas supplyline 6 has a straight portion between the growing section 3 b and thesecond heat shield plate 9B, and a bent portion between the second heatshield plate 9B and the upstream flange 8A.

The first and second heat shield plates 9A, 9B may be made of e.g.quartz or carbon. The second heat shield plate 9B on the side of (i.e.closer to) the gas inlet 64 a is preferably made of quartz, while thefirst heat shield plate 9A on the side of (i.e. closer to) the growingsection 3 b is preferably made of carbon. In addition, although the heatshielding effect is enhanced in accordance with the increase in numberof the heat shield plates 9A, 9B, the heat shielding effect may bedeteriorated if the number of the heat shield plates 9A, 9B is toolarge. Therefore, it is preferable that the number of the heat shieldingplates 9 is approximately 2 to 5.

The effect is enhanced in accordance with the increase in eccentricity(i.e. a distance between a center of the straight portion and a centerof the bent portion) of the gas inlet pipe 60. In this embodiment, thegas inlet pipe 60 is eccentrically configured (bent) for about 10 to 20mm. It is preferable that the gas inlet pipe 60 is eccentricallyconfigured such that the eccentricity thereof is not less than a lengthof a diameter of the gas inlet pipe 60. When the gas inlet pipe 60 has adiameter of 10 mm, the eccentricity thereof is preferably at least 10mm. When the gas inlet pipe 60 has a diameter of 20 mm, the eccentricitythereof is preferably at least 20 mm.

Effects of the First Embodiment

According to the present embodiment, since it is possible to suppressthe temperature rise in vicinity of the gas inlet 64 a (the upstream end64) of the gas inlet pipe 60, it is possible to suppress the interfusionof impurities into the gas inlet pipe 60 from the upstream end 64 madeof SUS.

Second Embodiment

FIG. 2 is a cross-sectional view of a nitride semiconductor template 10according to a second embodiment of the present invention.

A nitride semiconductor template 10 is produced with using the HVPEapparatus 1 as shown in FIG. 1. The nitride semiconductor template 10has a sapphire substrate 11, an MN buffer layer 12 formed on thesapphire substrate 11, an undoped GaN layer 13 formed as a first layeron the MN buffer layer 12, and a Si-doped GaN layer 14 formed as asecond layer on the undoped GaN layer 13. The undoped GaN layer 13 andSi-doped GaN layer 14 are an example of the template portion in thenitride semiconductor template.

If the template portion of the nitride semiconductor template 10consists of undoped GaN layer, the crystallinity will be improved. Thenitride semiconductor template 10, however, has a portion through whichcurrent flows, so that it is naturally necessary to dope the GaN layerwith n-type impurities such as Si. Here, Si concentration of theSi-doped GaN layer 14 of the nitride semiconductor template 10 ispreferably 5×10¹⁸ cm⁻³ to 5×10¹⁹ cm⁻³ for this purpose. In thisembodiment, the Si concentration is 1×10¹⁹ cm⁻³. Namely, this embodimentis not configured to improve the crystallinity by lowering the Siconcentration, but configured to suppress the contamination byunintended impurities even with the Si concentration in the order of10¹⁹ cm⁻³, thereby narrow the full width at half maximum (FWHM) of a(0004) plane of X-ray diffraction (XRD), to provide the nitridesemiconductor template with excellent crystallinity.

Effect of the Second Embodiment

According to the present embodiment of the invention, it is possible toprovide a nitride semiconductor template which can be suitably used inthe high efficiency semiconductor light-emitting device, by thedevelopment of metal chloride gas generator as described above which cansuppress the contamination by unintended impurities. In addition, it ispossible to significantly shorten the growth time by forming a nitridesemiconductor with using the HVPE method. As a result, it is possible toprovide a template for a high performance light-emitting device at a lowcost. Namely, this nitride semiconductor template is a template which isuseful for fabricating the high-brightness semiconductor light-emittingdevice.

Next, the present invention will be described in more detail by thefollowing examples. However, the present invention is not limitedthereto.

Example 1

First, Example 1 of the present invention will be explained below.

In Example 1, a nitride semiconductor template 10 as shown in FIG. 2 wasproduced with the use of the HVPE apparatus 1 as shown in FIG. 1. InExample 1, the second heat shield plate 9B made of quartz was providedon the side of the gas inlet 64 a as a first piece, and the first heatshield plate 9A made of carbon was provided on the side of the growingsection 3 b as a second piece.

As the sapphire substrate 11, a substrate having a thickness of 900 μmand a diameter of 100 mm (4 inches) was used. First, the AlN bufferlayer 12 having a film thickness of about 20 nm was formed on thesapphire substrate 11, the undoped GaN layer 13 was grown to have athickness of about 6 μm on the AlN buffer layer 12, and the Si-doped GaNlayer 14 was grown to have a thickness of about 2 μm on the undoped GaNlayer 13.

The HVPE growth was carried out as follows. After the sapphire substrate11 was set on the tray 5 of the HVPE apparatus 1, pure nitrogen wasflown thereinto to expel the air in the reactor 2. Next, the sapphiresubstrate 11 was held for 10 minutes at a substrate temperature of 1100degrees Celsius in a mixture gas of hydrogen at a flow rate of 3 slm anda nitrogen at a flow rate of 7 slm. Thereafter, hydrogen and nitrogen asthe carrier gas and trimethyl aluminum (TMA) were frown from the groupIII line 62, and NH₃ and hydrogen were flown from the group V line 61 togrow the AlN buffer layer 12. The undoped GaN layer 13 is further grownat a growth rate of 60 μm/hr. As to the flow rate of each gas for thisprocess, HCl, hydrogen and nitrogen were flown from the group III line62 at 50 sccm, 2 slm, and 1 slm, respectively, and NH₃ and hydrogen wereflown from the group V line 61 at 2 slm and 1 slm, respectively. Thegrowth time was 6 minutes.

After the undoped GaN layer 13 was grown as the first layer, theSi-doped GaN layer 14 was grown as the second layer by introducingdichlorosilane as Si material from the Si doping line 63 for 2 minutesunder the same basic growth conditions as those of the first layer.Thereafter, NH₃ and nitrogen were flown at 2 slm and 8 slm,respectively, and the substrate temperature was cooled down until arounda room temperature. Thereafter, the nitrogen purging was carried out forseveral dozens of minutes such that a nitrogen atmosphere was providedin the reactor 2, then the nitride semiconductor template 10 was takenout.

The full width at half maximum (FWHM) of the (0004) plane of the X-raydiffraction (XRD) of the nitride semiconductor template 10 in Example 1produced as described above was 237.8 seconds. To analyze theimpurities, SIMS analysis was also performed. The elements to beanalyzed by SIMS analysis were three kinds of elements, i.e. Fe, Cr andNi that are considered as impurities resulted from SUS.

FIG. 3 shows the results of SIMS analysis of Fe. For comparison with theconventional arts, FIG. 3 also shows the result of ComparativeExample 1. It was confirmed that the Fe concentration of the undoped GaNlayer (un-GaN) 13 and the Si-doped GaN layer (Si—GaN) 14 in Example 1was about 2×10¹⁵ cm⁻³ that is reduced by about two digit order than theFe concentration of 2.5×10¹⁷ cm⁻³ to 8.0×10¹⁷ cm⁻³ in ComparativeExample 1 to be described later.

FIG. 4 shows the results of SIMS analysis of Cr. For comparison with theconventional arts, FIG. 4 also shows the results of ComparativeExample 1. It was confirmed that the Cr concentration of the undoped GaNlayer (un-GaN) 13 and the Si-doped GaN layer (Si—GaN) 14 in Example 1was 1×10¹⁴ cm⁻³ (the lower detection limit is 2×10¹⁴ cm⁻³) that isreduced by about one digit order than the Cr concentration of about0.2×10¹⁵ cm⁻³ to 2×10¹⁵ cm⁻³ in Comparatice Example 1.

FIG. 5 shows the results of SIMS analysis of Ni. For comparison with theconventional arts, FIG. 5 also shows the results of ComparativeExample 1. It was confirmed that the Ni concentration of the undoped GaNlayer (un-GaN) 13 and the Si-doped GaN layer (Si—GaN) 14 in Example 1was the lower detection limit of SIMS analysis (i.e. 4×10¹⁵ cm⁻³),although the Cr concentration in Comparatice Example 1 was detectable bySIMS analysis.

Example 2

Example 2 of the present invention of the present invention will bedescribed below.

In Example 2, a nitride semiconductor template 10 as shown in FIG. 2 wasproduced with the use of the HVPE apparatus 1 as shown in FIG. 1. InExample 2, the nitride semiconductor template 10 was produced under thesimilar growth conditions as those in Example 1, except that HCl,hydrogen and nitrogen were flown from the group III gas line 62 at 50sccm, 2.5 slm, and 0.5 slm when growing the undoped GaN layer 13 and theSi-doped GaN layer 14. The full width at half maximum (FWHM) of the(0004) plane of the X-ray diffraction (XRD) of the nitride semiconductortemplate 10 was 203.8 seconds. As to the impurity concentration of theundoped GaN layer 13 and the Si-doped GaN layer 14, the Fe concentrationwas about 7.0×10¹⁴ cm⁻³ to 9.0×10¹⁵ cm⁻³, and the Cr concentration wasabout 6.0×10¹³ cm⁻³ to 8.0×10¹⁴ cm⁻³. The Ni concentration was kept to alower concentration than Comparative Example 1, similarly to Example 1.Thus, it is understood that the full width at half maximum (FWHM) of the(0004) plane became narrower.

It is confirmed that the full width at half maximum (FWHM) of the (0004)plane of the X-ray diffraction (XRD) was narrowed and that thecrystallinity was improved. Further, it is confirmed that the aboveeffects are provided by suppressing the contamination by unintendedimpurities. In addition, it is confirmed that Cl is contained in theundoped GaN layer 13 and the Si-doped GaN layer 14 grown by the HVPEapparatus 1.

From this result, it is confirmed that the quality of the nitridesemiconductor template 10 was improved by reducing the impurities. Toconfirm the effect of this result, semiconductor light-emitting deviceswere produced by performing an epitaxial growth using the MOVPE methodon the nitride semiconductor template 10 produced in Examples 1 and 2(see FIG. 7), respectively, and the effects thereof were confirmed.

(Method of Manufacturing a Semiconductor Light-Emitting Device)

Next, a method for manufacturing the semiconductor light-emitting devicewill be described below in conjunction with the drawings.

FIG. 6 shows a cross-sectional view of a semiconductor light-emittingdevice epitaxial wafer 20 in this embodiment, and FIG. 7 is across-sectional view of a semiconductor light-emitting device 30 in thisembodiment.

More specifically, an n-type GaN layer 21 was grown on the nitridesemiconductor template 10 as shown in FIG. 2, six pairs of InGaN/GaNmultiple quantum well layers 22 were grown on the n-type GaN layer 21, ap-type AlGaN layer 23 and a p-type GaN contact layer 24 were grown onthe InGaN/GaN multiple quantum well layers 22, and after the growth ofthe laminated structure described above, the temperature of the reactor2 was lowered to near the room temperature, then a semiconductorlight-emitting device epitaxial wafer 20 as shown in FIG. 6 was takenout from the MOVPE apparatus.

Thereafter, a surface of the semiconductor light-emitting deviceepitaxial wafer 20 thus obtained was partially removed by RIE (ReactiveIon Etching) to expose a part of the n-type Si-doped GaN layer 14 of thenitride semiconductor template 10, and a Ti/Al electrode 31 was formedthereon. Further, a Ni/Au semi-transparent electrode 32 and an electrodepad 33 were formed on the p-type GaN contact layer 24, to provide asemiconductor light-emitting device 30 as shown in FIG. 7.

The emission characteristic of the semiconductor light-emitting device30 was evaluated at a flowing current of 20 mA. The emission peakwavelength was about 450 nm, a forward voltage was 3.25 V, and theemission output was 15 mW. In addition, the reliability test of thesemiconductor light-emitting device 30 was carried out by electriccurrent applying test for 1000 hr at a flowing current of 50 mA and at aroom temperature. As a result, the relative output was 98%, so that asufficiently good reliability characteristic was confirmed. Here,“relative output”=“(emission output after current flow for 168hours/initial emission output)×100”.

Comparative Example 1

FIG. 8 shows an HVPE apparatus 100 according to Comparative Example 1.As Comparative Example 1, an HVPE apparatus 100 as shown in FIG. 8 wasused.

The HVPE apparatus 100 in Comparative Example 1 is configured similar tothe HVPE apparatus 1 shown in FIG. 1, except that the gas supply line 6has a straight pipe structure, and the heat shield plates 9A, 9B are notprovided.

Structure of the nitride semiconductor template 10 fabricated inComparative Example 1 is the same as that in Example 1 as shown in FIG.1, and the growth conditions are also same as those in Example 1.Further, structure, manufacturing conditions and growth conditions of asemiconductor light-emitting device epitaxial wafer 20 (see FIG. 6) anda semiconductor light-emitting device 30 (see FIG. 7) fabricated inComparative Example 1 are the same as those in Example 1. All featuresare the same as those in Example 1 except the structure of the HVPEapparatus.

The full width at half maximum (FWHM) of the (0004) plane of the X-raydiffraction (XRD) of the nitride semiconductor template 10 produced asdescribed above was 450.1 seconds. It is understood that the full widthat half maximum (FWHM) in Example 1 was approximately halved incomparison with Comparative Example 1. The explanation with respect tothe impurity concentration (see FIGS. 3 to 5) is omitted because it isalready described in relation to Example 1.

The emission characteristic of the semiconductor light-emitting device30 was evaluated at a flowing current of 20 mA. The emission peakwavelength was about 452 nm, a forward voltage was 3.21 V, and theemission output was 10 mW. Namely, due to the contamination byimpurities such as Fe, Cr, and Ni, the crystal defects were increased.As a result, the full width at half maximum was broadened, so that aninternal quantum efficiency was deteriorated, thereby the emissionoutput was lowered. In other words, the contamination by impurities wassuppressed in Example 1, so that the internal quantum efficiency wasenhanced, thereby the emission output was increased.

Further, the reliability test of the semiconductor light-emitting device30 in Comparative Example 1 was also carried out by electric currentapplying test for 1000 hr at a flowing current of 50 mA and at a roomtemperature. As a result, the relative output was 83%, so that it wasconfirmed that the reliability characteristic was not so good. It isobvious that the reliability was not good due to the poor crystallinity.Here, “relative output”=“(emission output after current flow for 168hours/initial emission output)×100”.

Comparative Example 2

As Comparative Example 2, the HVPE apparatus 100 as shown in FIG. 8 wasused. Structure of the nitride semiconductor template 10 fabricated inComparative Example 2 is the same as that in Example 1 as shown in FIG.1, and the growth conditions are also same as those in Example 1.Further, structure, manufacturing conditions and growth conditions of asemiconductor light-emitting device epitaxial wafer 20 (see FIG. 6) anda semiconductor light-emitting device 30 (see FIG. 7) fabricated inComparative Example 2 are the same as those in Example 1.

However, the growth temperature was set to 900 degrees Celsius forsuppressing the contamination by unintended impurities. Namely, allfeatures are the same as those in Example 1 except that the temperatureof the growing section 3 b is 900 degrees Celsius.

The full width at half maximum (FWHM) of the (0004) plane of the X-raydiffraction (XRD) of the nitride semiconductor template 10 produced asdescribed above was 432.5 seconds. The impurity concentrations are notshown but slightly more than those in Example 1. Namely, thecontamination by unintended impurities was lowered by lowering thegrowth temperature, but the full width at half maximum (FWHM) of the(0004) plane was broadened.

The emission characteristic of the semiconductor light-emitting device30 was evaluated at a flowing current of 20 mA. The emission peakwavelength was about 451 nm, a forward voltage was 3.22 V, and theemission output was 10 mW. Namely, when the contamination by impuritiessuch as Fe, Cr, and Ni is suppressed by lowering the growth temperature,the crystal defects were increased. As a result, the full width at halfmaximum is broadened, so that an internal quantum efficiency wasdeteriorated, thereby the emission output was lowered.

Further, the reliability test of the semiconductor light-emitting device30 in Comparative Example 2 was also carried out by electric currentapplying test for 1000 hr at a flowing current of 50 mA and at a roomtemperature. As a result, the relative output was 84%, so that it wasconfirmed that the reliability characteristic was not so good. It isobvious that the reliability was not good due to the poor crystallinity.Here, “relative output”=“(emission output after current flow for 168hours/initial emission output)×100”.

(Variation 1)

In the embodiment of the present invention, a flat sapphire substratewas used. The same effect can also be obtained by using a so-called PSS(Patterned Sapphire Substrate) in which an uneven surface is formed onthe sapphire substrate.

(Variation 2)

In the embodiment of the present invention, the growth rate was 60μm/hr. The growth rate increased up to about 300 μm/hr is alsoapplicable.

(Variation 3)

Since the present invention relates to a GaN film provided on thesubstrate, the intended effect of the present invention also can beobtained by using a buffer layer made of a material other than AlN.

(Variation 4)

FIG. 9 is a cross-sectional view illustrating a Schottky barrier diode40 according to a Variation 4 of the present invention. A Schottkybarrier diode 40 has a sapphire substrate 41, and an n-type GaN layer 43grown to have a thickness of 3.5 to 8 μm on the sapphire substrate 41,and an ohmic electrodes 45 and a Schottky electrode 46 formed on then-type GaN layer 43.

The n-type GaN layer 43 is doped with e.g. Si, and the carrierconcentration is 4×10¹⁷ cm⁻³.

The ohmic electrode 45 has a two-layer structure made of Ti/Al, in whicha Ti layer having a thickness of e.g. 20 nm and an Al layer having athickness of e.g. 200 nm are formed in this order on the n-type GaNlayer 43.

The Schottky electrode 46 has a two-layer structure made of Ni/Au, inwhich a Ni layer having a thickness of e.g. 50 nm and a Au layer havinga thickness of e.g. 500 nm are formed in this order on the n-type GaNlayer 43.

In addition, the present invention is not limited to the aboveembodiments, examples, and variations, and it is possible to implementvarious modifications without going beyond the gist of the invention.For example, in the above embodiment and examples, the case of applyinga metal chloride gas generator to the HVPE method is described, however,the present invention is not limited thereto, and may be applied toother growing methods.

Although the invention has been described with respect to the specificembodiments for complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A nitride semiconductor template, comprising: asubstrate; and a chlorine-containing nitride semiconductor layer,wherein the chlorine-containing nitride semiconductor layer contains aniron concentration of not higher than 1×10¹⁷ cm⁻³.
 2. The nitridesemiconductor template according to claim 1, wherein a full width athalf maximum of a (0004) plane of X-ray diffraction is not less than 200seconds and not more than 300 seconds.
 3. The nitride semiconductortemplate according to claim 1, wherein the chlorine-containing nitridesemiconductor layer comprises a Si-doped GaN layer containing a Siconcentration of not less than 5×10¹⁸ cm⁻³ and not more than 5×10¹⁹cm⁻³.